WO2014119222A1

WO2014119222A1 - Fuel cell module

Info

Publication number: WO2014119222A1
Application number: PCT/JP2013/085351
Authority: WO
Inventors: Tetsuya Ogawa; Yuki Yoshimine
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2013-01-30
Filing date: 2013-12-27
Publication date: 2014-08-07
Anticipated expiration: 2015-07-30
Also published as: JP6051065B2; JP2014146578A

Abstract

A fuel cell module (12) includes an inner area where an exhaust gas combustor (52) and a start-up combustor (54) are provided, and an annular outer area around the inner area and where a reformer (46), an evaporator (48), and a heat exchanger (50) are provided. Each of reforming pipes (66) of the reformer (46) includes a reforming catalyst filled space (69a) provided on a side closer to a reformed gas discharge chamber (78b), and a non-reforming catalyst filled space (69b) provided on a side closer to a mixed gas supply chamber (78a). The reforming catalyst filled space (69a) is filled with reforming catalyst (67a) for facilitating reforming reaction of the mixed gas, and the non-reforming catalyst filled space (69b) is filled with non-reforming catalyst (67b) for facilitating raise in the temperature of the mixed gas and diffusion of the mixed gas.

Description

DESCRIPTION

Title of Invention

FUEL CELL MODULE

Technical Field

The present invention relates to a fuel cell module including a fuel cell stack formed by stacking a plurality of fuel cells for generating electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas.

Background Art

Typically, a solid oxide fuel cell (SOFC) employs a solid electrolyte of ion-conductive solid oxide such as stabilized zirconia. The solid electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (hereinafter also referred to as MEA) .

The electrolyte electrode assembly is sandwiched between separators (bipolar plates). In use, generally,

predetermined numbers of the electrolyte electrode

assemblies and the separators are stacked together to form a fuel cell stack.

As a system including this fuel cell stack, for

example, a fuel cell battery disclosed in Japanese Laid-Open Patent Publication No. 2001-236980 (hereinafter referred to as the conventional technique 1) is known. As shown in FIG.

12, the fuel cell battery includes a fuel cell stack la, and a heat insulating sleeve 2a is provided at one end of the fuel cell stack la. A reaction device 4a is provided in the heat insulating sleeve 2a. The reaction device 4a includes a heat exchanger 3a.

In the reaction device 4a, as a treatment of liquid fuel, partial oxidation reforming which does not use water is performed. After the liquid fuel is evaporated by an exhaust gas, the liquid fuel passes through a feeding point 5a which is part of the heat exchanger 3a. The fuel

contacts an oxygen carrier gas heated by the exhaust gas thereby to induce partial oxidation reforming, and then, the fuel is supplied to the fuel cell stack la.

Further, as shown in FIG. 13, a solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2010- 504607 (PCT) (hereinafter referred to as the conventional technique 2) has a heat exchanger 2b including a cell core lb. The heat exchanger 2b heats the cathode air utilizing waste heat.

Further, as shown in FIG. 14, a fuel cell system disclosed in Japanese Laid-Open Patent Publication No. 2004- 288434 (hereinafter referred to as the conventional

technique 3) includes a first area lc having a circular cylindrical shape extending vertically, and an annular second area 2c around the first area lc, an annular third area 3c around the second area 2c, and an annular fourth area 4c around the third area 3c .

A burner 5c is provided in the first area lc, and a reforming pipe 6c is provided in the second area 2c. A water evaporator 7c is provided in the third area 3c, and a CO shift converter 8c is provided in the fourth area 4c.

Furthermore, as shown in FIG. 15, a hydrogen generator disclosed in Japanese Laid-Open Patent Publication No. 2011- 037684 (hereinafter referred to as the conventional technique 4) includes a burner Id for combusting a fuel gas, a combustion gas channel 2d as a passage of a combustion exhaust gas from the burner Id, and a reforming catalyst layer 5d provided outside the combustion gas channel 2d.

The reforming catalyst layer 5d is composed of a cylinder 3d and a cylinder 4d. The reforming catalyst layer 5d is filled with catalyst including reforming catalyst 6d which is present on the upstream side of the flowing direction of the reformed gas, and reforming catalyst 7d which is present on the downstream side of the flowing direction of the reformed gas. The grain size of the reforming catalyst 7d is larger than the grain size of the reforming catalyst 6d.

Further, in a fuel reforming device disclosed in

Japanese Laid-Open Patent Publication No. 2001-151502

(hereinafter referred to as the conventional technique 5), as shown in FIG. 16, a fuel reformer 4e includes a main container le in the form of a container, the main container le being filled with catalytic fillers 2e and refractory fillers 3e. The catalytic fillers 2e and the refractory fillers 3e are formed into a predetermined shape so as to disturb the flow of a raw material gas. Each of the

catalytic fillers 2e supports catalyst which induces partial oxidation reaction. The catalytic fillers 2e and the refractory fillers 3e are mixedly present in the main container le.

Summary of Invention

In the conventional technique 1, at the time of

reforming by partial oxidation in the reaction device 4a, heat of the exhaust gas is used for heating the liquid fuel and the oxygen carrier gas. Therefore, the quantity of heat energy for raising the temperature of the oxygen-containing gas supplied to the fuel cell stack la tends to be

inefficient, and the efficiency is low.

Further, in the conventional technique 2, in order to increase heat efficiency, long flow channels are adopted to have a sufficient heat transmission area. Therefore, considerably high pressure losses tend to occur.

Further, in the conventional technique 3, radiation of the heat from the central area having the highest

temperature is suppressed using heat insulation material (partition wall). Therefore, heat cannot be recovered, and the efficiency is low.

Furthermore, in the conventional technique 4, the reforming catalyst 6d having a small grain size, i.e., low compressive breaking strength, is provided on the upstream side in the flowing direction in the reforming catalyst layer 5d. Thus, in the reforming catalyst 6d, if the catalyst is damaged or pulverized, clogging may occur on the downstream side. Further, the raw material gas is supplied to the cylindrical reforming catalyst layer 5d from a raw material gas supply unit 8d on one side. Therefore, nonuniform flow occurs easily in the reforming catalyst layer 5d, and reforming performance tends to be lowered easily.

Further, in the conventional technique 5, it is

extremely difficult to uniformly mix the catalytic fillers 2e and the refractory fillers 3e having two kinds of

spherical shapes in the same space of the main container le. Therefore, the mixed state of the catalytic fillers 2e and the refractory fillers 3e tends to vary, and reforming may not be conducted uniformly. Consequently, the performance is degraded due to the non-uniform reforming.

The present invention has been made to solve the problems of this type, and an object of the present

invention is to provide a fuel cell module having simple and compact structure in which it is possible to achieve

improvement in the heat efficiency and facilitation of thermally self-sustaining operation and also it is possible to conduct reforming efficiently.

The present invention relates to a fuel cell module including a fuel cell stack formed by stacking a plurality of fuel cells for generating electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas, a reformer for reforming a mixed gas of a raw fuel chiefly containing hydrocarbon and water vapor to produce the fuel gas supplied to the fuel cell stack, an evaporator for evaporating water, and supplying the water vapor to the reformer, a heat exchanger for raising the temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing gas to the fuel cell stack, an exhaust gas combustor for combusting the fuel gas discharged from the fuel cell stack as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack as an oxygen-containing exhaust gas to produce the combustion gas, and a start-up combustor for combusting the raw fuel and the oxygen-containing gas to produce the combustion gas .

The fuel cell module includes an inner area where the exhaust gas combustor and the start-up combustor are

provided, and an annular outer area around the inner area and where the reformer, the evaporator, and the heat

exchanger are provided.

The reformer includes an annular mixed gas supply chamber to which the mixed gas is supplied, an annular reformed gas discharge chamber to which the produced fuel gas is discharged, a plurality of reforming pipes each having one end connected to the mixed gas supply chamber, and another end connected to the reformed gas discharge chamber, and a combustion gas channel for supplying the combustion gas to spaces between the reforming pipes.

Further, each of the reforming pipes includes a reforming catalyst filled space provided on a side closer to the reformed gas discharge chamber and a non-reforming catalyst filled space provided on a side closer to the mixed gas supply chamber. The reforming catalyst filled space is filled with reforming catalyst for facilitating reforming reaction of the mixed gas, and the non-reforming catalyst filled space is filled with non-reforming catalyst for facilitating raise in the temperature of the mixed gas and diffusion of the mixed gas.

In the present invention, the inner area containing the exhaust gas combustor and the start-up combustor is

centrally-located. The annular outer area is then provided around the inner area. The reformer, the evaporator, and the heat exchanger are provided in the outer area. In the structure, heat waste and heat radiation can be suppressed suitably. Thus, improvement in the heat efficiency is achieved, and thermally self-sustaining operation is

facilitated. Further, simple and compact structure of the fuel cell module is achieved as a whole. Further, in the reformer, the annular mixed gas supply chamber, the annular reformed gas discharge chamber, and the reforming pipes are provided as basic structure. Thus, simple structure is achieved easily. Accordingly, the production cost of the reformer is reduced effectively.

Further, by changing the volumes of the mixed gas supply chamber and the reformed gas discharge chamber, the length, the diameter, and the number of the pipes, a desired

operation can be achieved depending on various operating conditions, and the design flexibility of the fuel cell module can be enhanced.

Furthermore, in the reforming pipes, reforming catalyst for facilitating reforming reaction of the mixed gas is provided on the downstream side (closer to the reformed gas discharge chamber) , and non-reforming catalyst for

facilitating raise in the temperature of the mixed gas and diffusion of the mixed gas is provided on the upstream side (closer to the mixed gas supply chamber). Therefore, before the mixed gas reaches the reforming catalyst filled space, the mixed gas sufficiently increases in temperature and is sufficiently diffused by the non-reforming catalyst filled space. Accordingly, owing to maintaining of the reforming temperature in the reforming catalyst filled space,

improvement in the reforming efficiency is achieved, and it becomes possible to reliably suppress degradation of the durability due to the non-uniform flow of the mixed gas.

Further, before the mixed gas reaches the reforming catalyst filled space, flow of the mixed gas is disturbed in the non-reforming catalyst filled space. Accordingly, raise in the temperature of the mixed gas is facilitated, and thus the reforming temperature of the reforming catalyst is maintained. Therefore, the reforming efficiency is improved suitably.

The above and other objects features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. Brief Description of Drawings

FIG. 1 is a diagram schematically showing structure of a fuel cell system including a fuel cell module according to an embodiment of the present invention;

FIG. 2 is a perspective view showing FC peripheral equipment of the fuel cell module;

FIG. 3 is a cross sectional view showing the FC

peripheral equipment;

FIG. 4 is a perspective view with partial omission showing the FC peripheral equipment ;

FIG. 5 is an exploded perspective view showing main components of the FC peripheral equipment;

FIG. 6 is a cross sectional view showing the FC

peripheral equipment ;

FIG. 7 is a graph showing the state where the

temperature of the mixed gas is raised in the present embodiment and in a comparative example;

FIG. 8 is a graph illustrating the temperature at which reforming is started, depending on the ratio of the length of the non-reforming catalyst filled space to the length of the reforming catalyst filled space; FIG. 9 is a view showing the velocity of the mixed gas in a reforming pipe;

FIG. 10 is a graph illustrating the velocity ratio, depending on the ratio of the length of the non-reforming catalyst filled space to the length of the reforming catalyst filled space;

FIG. 11 is a graph showing the ratio of the pressure loss, depending on the ratio of the grain size of the non- reforming catalyst to the grain size of the reforming catalyst;

FIG. 12 is a view schematically showing a fuel cell battery disclosed in a conventional technique 1;

FIG. 13 is a perspective view with partial cutout showing a solid oxide fuel cell disclosed in a conventional technique 2;

FIG. 14 is a view schematically showing a fuel cell system disclosed in a conventional technique 3.

FIG. 15 is a view schematically showing a hydrogen generator disclosed in a conventional technique 4; and

FIG. 16 is a partial cross sectional perspective view showing a fuel reforming device disclosed in a conventional technique 5.

Description of Embodiments

As shown in FIG. 1, a fuel cell system 10 includes a fuel cell module 12 according to an embodiment of the present invention, and the fuel cell system 10 is used in various applications, including stationary and mobile applications. For example, the fuel cell system 10 is mounted on a vehicle. The fuel cell system 10 includes the fuel cell module (SOFC module) 12 for generating electrical energy in power generation by electrochemical reactions of a fuel gas (a gas produced by mixing a hydrogen gas , methane , and carbon monoxide) and an oxygen-containing gas (air), a raw fuel supply apparatus (including a fuel gas pump) 14 for

supplying a raw fuel (e.g., city gas) to the fuel cell module 12, an oxygen-containing gas supply apparatus

(including an air pump) 16 for supplying the oxygen- containing gas to the fuel cell module 12, a water supply apparatus (including a water pump) 18 for supplying water to the fuel cell module 12, and a control device 20 for

controlling the amount of electrical energy generated in the fuel cell module 12.

The fuel cell module 12 includes a solid oxide fuel cell stack 24 formed by stacking a plurality of solid oxide fuel cells 22 in a vertical direction (or horizontal

direction) . The fuel cell 22 includes an electrolyte electrode assembly (MEA) 32. The electrolyte electrode assembly 32 includes a cathode 28, an anode 30, and an electrolyte 26 interposed between the cathode 28 and the anode 30. For example, the electrolyte 26 is made of ion- conductive solid oxide such as stabilized zirconia.

A cathode side separator 34 and an anode side separator 36 are provided on both sides of the electrolyte electrode assembly 32. An oxygen-containing gas flow field 38 for supplying the oxygen-containing gas to the cathode 28 is formed in the cathode side separator 34, and a fuel gas flow field 40 for supplying the fuel gas to the anode 30 is formed in the anode side separator 36. As the fuel cell 22, various types of conventional SOFCs can be adopted.

The operating temperature of the fuel cell 22 is high, that is, several hundred °C. Methane in the fuel gas is reformed at the anode 30 to obtain hydrogen and CO, and the hydrogen and CO are supplied to a portion of the electrolyte 26 adjacent to the anode 30.

An oxygen-containing gas supply passage 42a, an oxygen- containing gas discharge passage 42b, a fuel gas supply passage 44a, and a fuel gas discharge passage 44b extend through the fuel cell stack 24. The oxygen-containing gas supply passage 42a is connected to an inlet of each oxygen- containing gas flow field 38, the oxygen-containing gas discharge passage 42b is connected to an outlet of each oxygen-containing gas flow field 38, the fuel gas supply passage 44a is connected to an inlet of each fuel gas flow field 40, and the fuel gas discharge passage 44b is

connected to an outlet of each fuel gas flow field 40.

The fuel cell module 12 includes a reformer 46 for reforming a mixed gas of a raw fuel chiefly containing hydrocarbon (e.g., city gas) and water vapor to produce a fuel gas supplied to the fuel cell stack 24, an evaporator 48 for evaporating water and supplying the water vapor to the reformer 46, a heat exchanger 50 for raising the

temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing gas to the fuel cell stack 24, an exhaust gas combustor 52 for combusting the fuel gas discharged from the fuel cell stack 24 as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack 24 as an oxygen- containing exhaust gas to produce the combustion gas, and a start-up combustor 54 for combusting the raw fuel and the oxygen-containing gas to produce the combustion gas.

Basically, the fuel cell module 12 is made up of the fuel cell stack 24 and FC (fuel cell) peripheral equipment (BOP) 56 (see FIGS. 1 and 2). The FC peripheral equipment 56 includes the reformer 46, the evaporator 48, the heat exchanger 50, the exhaust gas combustor 52, and the start-up combustor 54.

As shown in FIGS. 3 to 5, the FC peripheral equipment 56 includes a first area (inner area) Rl where the exhaust gas combustor 52 and the start-up combustor 54 are provided, an annular second area (outer area) R2 formed around the first area Rl and where the reformer 46 and the evaporator 48 are provided, and an annular third area (outer area) R3 formed around the second area R2 and where the heat

exchanger 50 is provided. A cylindrical outer member 55 constituting an outer wall is provided on the outer

peripheral side of the third area R3.

In the second area R2 , the reformer 46 may be provided on the inner side in the radial direction and the heat exchanger 50 may be provided on the outer side in the radial direction, and in the third area R3, the evaporator 48 may be provided. Alternatively, in the second area R2 , the heat exchanger 50 may be provided on the inner side in the radial direction and the reformer 46 may be provided on the outer side in the radial direction, and in the third area R3, the evaporator 48 may be provided.

The start-up combustor 54 is provided at the other end distant from the fuel cell stack 24, and includes an air supply pipe 57 and a raw fuel supply pipe 58. The start-up combustor 54 has an ejector function, and generates negative pressure in the raw fuel supply pipe 58 by the flow of the air supplied from the air supply pipe 57 for sucking the raw fuel .

The exhaust gas combustor 52 is provided at one end adjacent to the fuel cell stack 24, and has a combustion cup member 60 at a position spaced away from the start-up combustor 54. The combustion cup member 60 is attached to a support portion 62 such that the combustion cup member 60 is oriented from the fuel cell stack 24 toward the start-up combustor 54 (first area Rl).

A plurality of holes (e.g., circular holes or

rectangular holes) 60a, which are combustion gas holes, are formed along the outer circumference of the marginal end of the combustion cup member 60 on the bottom side (i.e., the side adjacent to a bottom 60e). One end of an oxygen- containing exhaust gas channel 63a and one end of a fuel exhaust gas channel 63b are provided at the combustion cup member 60. The combustion gas is produced inside the combustion cup member 60 by combustion reaction of the fuel gas (more specifically, fuel exhaust gas) and the oxygen- containing gas (more specifically, oxygen-containing exhaust gas) .

As shown in FIG. 1, the other end of the oxygen- containing exhaust gas channel 63a is connected to the oxygen-containing gas discharge passage 42b of the fuel cell stack 24, and the other end of the fuel exhaust gas channel 63b is connected to the fuel gas discharge passage 44b of the fuel cell stack 24.

As shown in FIGS. 3 to 5, the reformer 46 is a preliminary reformer for reforming higher hydrocarbon (C₂₊) such as ethane (C₂H₆), propane (C₃H₈), and butane ( C₄Hi₀ ) in the city gas (raw fuel) to produce the fuel gas chiefly containing methane (CH₄), hydrogen, and CO by steam

reforming. The operating temperature of the reformer 46 is set at several hundred °C.

The reformer 46 includes a plurality of reforming pipes (heat transmission pipes) 66 provided around the exhaust gas combustor 52 and the start-up combustor 54. Each of the reforming pipes 66 includes a reforming catalyst filled space 69a provided on the downstream side in the flow direction of the mixed gas (i.e., on a side closer to a reformed gas discharge chamber 78b described later) and a non-reforming catalyst filled space 69b provided on the upstream side in the flow direction of the mixed gas (i.e., on a side closer to a mixed gas supply chamber 78a described later) . The reforming catalyst filled space 69a is filled with reforming catalyst 67a for facilitating reforming reaction of the mixed gas, and the non-reforming catalyst filled space 69b is filled with non-reforming catalyst 67b for facilitating raise in the temperature of the mixed gas and diffusion of the mixed gas .

The volume Wl of the reforming catalyst filled space 69a is larger than the volume W2 of the non-reforming catalyst filled space 69b (Wl > W2). The volume Wl of the reforming catalyst filled space 69a and the volume W2 of the non-reforming catalyst filled space 69b have the

relationship where 0.1 ≤ W2/W1 ≤ 0.2.

The reforming pipe 66 has a cylindrical shape having a constant opening-diameter in the axial direction. The length LI of the reforming catalyst filled space 69a in the axial direction is larger than the length L2 of the non- reforming catalyst filled space 69b in the axial direction (LI > L2). The length LI of the reforming catalyst filled space 69a and the length L2 of the non-reforming catalyst filled space 69b have the relationship where 0.1 ≤ L2/L1 ≤ 0.2.

Each of the reforming catalyst 67a and the non- reforming catalyst 67b contains pellets of ceramics such as alumina (aluminum oxide) (A1₂0₃) as base bodies. The base bodies of the reforming catalyst 67a and the non-reforming catalyst 67b have the same size, and the same shape. In the reforming catalyst 67a, reforming agent, e.g., ruthenium or nickel, is supported on the base body by impregnation. The grain size of the reforming catalyst 67a is larger than the grain size of the non-reforming catalyst 67b.

Metal meshes kl , k2 are provided at both ends of each of the reforming pipes 66 for preventing dropping-out of the reforming catalyst 67a and the non-reforming catalyst 67b. Each of the reforming pipes 66 has one end (lower end) fixed to a first lower ring member 68a, and the other end (upper end) fixed to a first upper ring member 68b.

The outer circumferential portions of the first lower ring member 68a and the first upper ring member 68b are fixed to the inner circumferential surface of a cylindrical member 70 by welding or the like. The inner circumferential portions of the first lower ring member 68a and the first upper ring member 68b are fixed to the outer circumferential portions of the exhaust gas combustor 52 and the start-up combustor 54 by welding or the like. The cylindrical member 70 extends in an axial direction indicated by an arrow A, and an end of the cylindrical member 70 adjacent to the fuel cell stack 24 is fixed to the support portion 62. A

plurality of openings 72 are formed in the outer

circumference of the cylindrical member 70 in a

circumferential direction at predetermined height positions.

The evaporator 48 has evaporation pipes (heat

transmission pipes) 74 provided adjacent to, and outside the reforming pipes 66 of the reformer 46. As shown in FIG. 6, the reforming pipes 66 are arranged at equal intervals on a virtual circle, concentrically around the first area Rl.

The evaporation pipes 74 are arranged at equal intervals on a virtual circle, concentrically around the first area Rl. The number of the evaporation pipes 74 is half of the number of the reforming pipes 66. The evaporation pipes 74 are positioned on the back side of every other position of the reforming pipe 66 (i.e., at positions spaced away from the center of the first area Rl). The holes 60a are oriented toward positions between the reforming pipes 66 of the reformer 46. Alternatively, the holes 60a may be oriented toward the reforming pipes 66.

As shown in FIGS. 3 and 4, each of the evaporation pipes 74 has one end (lower end) which is fixed to a second lower ring member 76a by welding or the like, and the other end (upper end) which is fixed to a second upper ring member 76b by welding or the like. The outer circumferential portions of the second lower ring member 76a and the second upper ring member 76b are fixed to the inner circumferential surface of the cylindrical member 70 by welding or the like. The inner circumferential portions of the second lower ring member 76a and the second upper ring member 76b are fixed to the outer circumferential portions of the exhaust gas combustor 52 and the start-up combustor 54 by welding or the like .

The second lower ring member 76a is positioned below the first lower ring member 68a (i.e., outside the first lower ring member 68a in the axial direction) , and the second upper ring member 76b is positioned above the first upper ring member 68b (i.e., outside the first upper ring member 68b in the axial direction).

An annular mixed gas supply chamber 78a is formed between the first lower ring member 68a and the second lower ring member 76a, and a mixed gas of raw fuel and water vapor is supplied to the mixed gas supply chamber 78a. Further, an annular reformed gas discharge chamber 78b is formed between the first upper ring member 68b and the second upper ring member 76b, and the produced fuel gas (reformed gas) is discharged to the reformed gas discharge chamber 78b. Both ends of each of the reforming pipes 66 are opened to the mixed gas supply chamber 78a and the reformed gas discharge chamber 78b.

A ring shaped end ring member 80 is fixed to an end of the cylindrical member 70 on the start-up combustor 54 side by welding or the like. An annular water supply chamber 82a is formed between the end ring member 80 and the second lower ring member 76a, and water is supplied to the water supply chamber 82a. An annular water vapor discharge chamber 82b is formed between the second upper ring member 76b and the support portion 62, and water vapor is

discharged to the water vapor discharge chamber 82b. Both ends of each of the evaporation pipes 74 are opened to the water supply chamber 82a and the water vapor discharge chamber 82b.

The reformed gas discharge chamber 78b and the water vapor discharge chamber 82b are provided in a double deck manner, and the reformed gas discharge chamber 78b is provided on the inner side with respect to the water vapor discharge chamber 82b (i.e., below the water vapor discharge chamber 82b). The mixed gas supply chamber 78a and the water supply chamber 82a are provided in a double deck manner, and the mixed gas supply chamber 78a is provided on the inner side with respect to the water supply chamber 82a (i.e., above the water supply chamber 82a).

A raw fuel supply channel 84 is opened to the mixed gas supply chamber 78a, and an evaporation return pipe 90 described later is connected to a position in the middle of the raw fuel supply channel 84 (see FIG. 1). The raw fuel supply channel 84 has an ejector function, and generates negative pressure by the flow of the raw fuel for sucking the water vapor.

The raw fuel supply channel 84 is fixed to the second lower ring member 76a and the end ring member 80 by welding or the like. One end of a fuel gas channel 86 is connected to the reformed gas discharge chamber 78b, and the other end of the fuel gas channel 86 is connected to the fuel gas supply passage 44a of the fuel cell stack 24 (see FIG. 1). The fuel gas channel 86 is fixed to the second upper ring member 76b by welding or the like, and extends through the support portion 62 (see FIG. 2).

A water channel 88 is connected to the water supply chamber 82a. The water channel 88 is fixed to the end ring member 80 by welding or the like. One end of the

evaporation return pipe 90 formed by at least one

evaporation pipe 74 is provided in the water vapor discharge chamber 82b, and the other end of the evaporation return pipe 90 is connected to a position in the middle of the raw fuel supply channel 84 (see FIG. 1).

As shown in FIGS. 3 and 4, the heat exchanger 50 includes a plurality of heat exchange pipes (heat

transmission pipes) 96 which are provided along and around the outer circumference of the cylindrical member 70. Each of the heat exchange pipes 96 has one end (lower end) fixed to a lower ring member 98a, and the other end (upper end) fixed to an upper ring member 98b.

A lower end ring member 100a is provided below the lower ring member 98a, and an upper end ring member 100b is provided above the upper ring member 98b. The lower end ring member 100a and the upper end ring member 100b are fixed to the outer circumference of the cylindrical member 70 and the inner circumference of the outer member 55 by welding or the like.

An annular oxygen-containing gas supply chamber 102a to which the oxygen-containing gas is supplied is formed between the lower ring member 98a and the lower end ring member 100a. An annular oxygen-containing gas discharge chamber 102b is formed between the upper ring member 98b and the upper end ring member 100b. The heated oxygen- containing gas is discharged to the oxygen-containing gas discharge chamber 102b. Both ends of each of the heat exchange pipes 96 are fixed to the lower ring member 98a and the upper ring member 98b by welding or the like, and opened to the oxygen-containing gas supply chamber 102a and the oxygen-containing gas discharge chamber 102b.

The mixed gas supply chamber 78a and the water supply chamber 82a are placed on the radially inward side relative to the inner circumference of the oxygen-containing gas supply chamber 102a. The oxygen-containing gas discharge chamber 102b is provided outside the reformed gas discharge chamber 78b at a position offset downward from the reformed gas discharge chamber 78b.

A cylindrical cover member 104 is provided on the outer circumferential portion of the outer member 55. The center position of the cylindrical cover member 104 is shifted downward. Both of upper and lower ends (both of axial ends) of the cover member 104 are fixed to the outer member 55 by welding or the like, and a heat recovery area (chamber) 106 is formed between the cover member 104 and the outer

circumferential surface of the outer member 55.

A plurality of holes 108 are formed circumferentially in a lower marginal end portion of the outer member 55 of the oxygen-containing gas supply chamber 102a, and the oxygen-containing gas supply chamber 102a communicates with the heat recovery area 106 through the holes 108. An oxygen-containing gas supply pipe 110 communicating with the heat recovery area 106 is connected to the cover member 104. An exhaust gas pipe 112 communicating with the third area R3 is connected to an upper portion of the outer member 55.

For example, one end of each of two oxygen-containing gas pipes 114 is provided in the oxygen-containing gas discharge chamber 102b. Each of the oxygen-containing gas pipes 114 has a stretchable member such as a bellows 114a between the upper end ring member 100b and the support portion 62. The other end of each of the oxygen-containing gas pipes 114 extends through the support portion 62, and is connected to the oxygen-containing gas supply passage 42a of the fuel cell stack 24 (see FIG. 1).

As shown in FIG. 3, a first combustion gas channel 116a as a passage of the combustion gas is formed in the first area Rl, and a second combustion gas channel 116b as a passage of the combustion gas that has passed through the holes 60a is formed in the second area R2. A third

combustion gas channel 116c as a passage of the combustion gas that has passed through the openings 72 is formed in the third area R3. Further, a fourth combustion gas channel 116d is formed as a passage after the exhaust gas pipe 112. The second combustion gas channel 116b forms the reformer 46 and the evaporator 48, and the third combustion gas channel 116c forms the heat exchanger 50.

As shown in FIG. 1, the raw fuel supply apparatus 14 includes a raw fuel channel 118. The raw fuel channel 118 is branched into the raw fuel supply channel 84 and the raw fuel supply pipe 58 through a raw fuel regulator valve 120. A desulfurizer 122 for removing sulfur compounds in the city gas (raw fuel) is provided in the raw fuel supply channel 84.

The oxygen-containing gas supply apparatus 16 includes an oxygen-containing gas channel 124. The oxygen-containing gas channel 124 is branched into the oxygen-containing gas supply pipe 110 and the air supply pipe 57 through an oxygen-containing gas regulator valve 126. The water supply apparatus 18 is connected to the evaporator 48 through the water channel 88.

Operation of the fuel cell system 10 will be described below.

At the time of starting operation of the fuel cell system 10, the air (oxygen-containing gas) and the raw fuel are supplied to the start-up combustor 54. More

specifically, by operation of the air pump, the air is supplied to the oxygen-containing gas channel 124. By adjusting the opening degree of the oxygen-containing gas regulator valve 126, the air is supplied to the air supply pipe 57.

In the meanwhile, in the raw fuel supply apparatus 14, by operation of the fuel gas pump, for example, raw fuel such as the city gas (containing CH₄, C₂H₆, C₃H₈, C₄Hi₀) is supplied to the raw fuel channel 118. By regulating the opening degree of the raw fuel regulator valve 120, the raw fuel is supplied into the raw fuel supply pipe 58. The raw fuel is mixed with the air, and supplied into the start-up combustor 54 (see FIGS. 3 and 4).

Thus , the mixed gas of the raw fuel and the air is supplied into the start-up combustor 54, and the mixed gas is ignited to start combustion. Therefore, the combustion gas produced in combustion flows from the first area Rl to the second area R2. Further, the combustion gas is supplied to the third area R3, and then, the combustion gas is discharged to the outside of the fuel cell module 12 through the exhaust gas pipe 112.

As shown in FIGS. 3 and 4, the reformer 46 and the evaporator 48 are provided in the second area R2, and the heat exchanger 50 is provided in the third area R3. Thus, the combustion gas discharged from the first area Rl first heats the reformer 46, next heats the evaporator 48, and then heats the heat exchanger 50.

Then, after the temperature of the fuel cell module 12 is raised to a predetermined temperature, the air (oxygen- containing gas) is supplied to the heat exchanger 50, and the mixed gas of the raw fuel and the water vapor is

supplied to the reformer 46.

More specifically, as shown in FIG. 1, the opening degree of the oxygen-containing gas regulator valve 126 is adjusted such that the flow rate of the air supplied to the oxygen-containing gas supply pipe 110 is increased, and the opening degree of the raw fuel regulator valve 120 is adjusted such that the flow rate of the raw fuel supplied to the raw fuel supply channel 84 is increased. Further, by operation of the water supply apparatus 18, the water is supplied to the water channel 88. The air is supplied from the oxygen-containing gas supply pipe 110 to the heat recovery area 106 of the outer member 55. Thus, the air flows through the holes 108 into the oxygen-containing gas supply chamber 102a.

Therefore, as shown in FIGS. 3 and 4, the air flows into the heat exchanger 50, and the air is temporarily supplied to the oxygen-containing gas supply chamber 102a.

Thereafter, while the air is moving inside the heat exchange pipes 96, the air is heated by heat exchange with the combustion gas supplied into the third area R3. After the heated air is temporarily supplied to the oxygen-containing gas discharge chamber 102b, the air is supplied to the oxygen-containing gas supply passage 42a of the fuel cell stack 24 through the oxygen-containing gas pipes 114 (see FIG. 1). In the fuel cell stack 24, the heated air flows along the oxygen-containing gas flow field 38, and the air is supplied to the cathode 28.

After the air flows through the oxygen-containing gas flow field 38, the air is discharged from the oxygen- containing gas discharge passage 42b into the oxygen- containing exhaust gas channel 63a. The oxygen-containing exhaust gas channel 63a is opened to the combustion cup member 60 of the exhaust gas combustor 52, and the oxygen- containing exhaust gas is supplied into the combustion cup member 60.

Further, as shown in FIG. 1, the water from the water supply apparatus 18 is supplied to the evaporator 48. After the raw fuel is desulfurized in the desulfurizer 122, the raw fuel flows through the raw fuel supply channel 84, and moves toward the reformer 46.

In the evaporator 48, after the water is temporarily supplied to the water supply chamber 82a, while water is moving inside the evaporation pipes 74, the water is heated by the combustion gas flowing through the second area R2 , and vaporized. After the water vapor flows into the water vapor discharge chamber 82b, the water vapor is supplied to the evaporation return pipe 90 connected to the water vapor discharge chamber 82b. Thus, the water vapor flows inside the evaporation return pipe 90, and flows into the raw fuel supply channel 84. Then, the water vapor is mixed with the raw fuel supplied by the raw fuel supply apparatus 14 to produce the mixed gas. The mixed gas from the raw fuel supply channel 84 is temporarily supplied to the mixed gas supply chamber 78a of the reformer 46. The mixed gas moves inside the reforming pipes 66. In the meanwhile, the mixed gas is heated by the combustion gas flowing through the second area R2 , and is then steam-reformed. After removal (reforming) of

hydrocarbon of C₂₊, a reformed gas chiefly containing

methane is obtained.

After this reformed gas is heated, the reformed gas is temporarily supplied to the reformed gas discharge chamber 78b as the fuel gas. Thereafter, the fuel gas is supplied to the fuel gas supply passage 44a of the fuel cell stack 24 through the fuel gas channel 86 (see FIG. 1). In the fuel cell stack 24, the heated fuel gas flows along the fuel gas flow field 40, and the fuel gas is supplied to the anode 30. In the meanwhile, the air is supplied to the cathode 28. Thus, electricity is generated in the electrolyte electrode assembly 32.

After the fuel gas flows through the fuel gas flow field 40, the fuel gas is discharged from the fuel gas discharge passage 44b to the fuel exhaust gas channel 63b. The fuel exhaust gas channel 63b is opened to the inside of the combustion cup member 60 of the exhaust gas combustor 52, and the fuel exhaust gas is supplied into the combustion cup member 60.

Under the heating operation by the start-up combustor 54, when the temperature of the fuel gas in the exhaust gas combustor 52 exceeds the self-ignition temperature,

combustion of the oxygen-containing exhaust gas and the fuel exhaust gas is started inside the combustion cup member 60. In the meanwhile, combustion operation by the start-up combustor 54 is stopped.

The holes 60a are formed in the combustion cup member 60. Therefore, the combustion gas supplied into the

combustion cup member 60 flows through the holes 60a from the first area Rl into the second area R2. Then, the combustion gas is supplied to the third area R3 , and

thereafter the combustion gas is discharged to the outside of the fuel cell module 12.

In the present embodiment, as shown in FIG. 3, each of the reforming pipes 66 includes the reforming catalyst filled space 69a provided on the side closer to the reformed gas discharge chamber 78b and the non-reforming catalyst filled space 69b provided on the side closer to the mixed gas supply chamber 78a. The reforming catalyst filled space 69a is filled with the reforming catalyst 67a for

facilitating reforming reaction of the mixed gas, and the non-reforming catalyst filled space 69b is filled with the non-reforming catalyst 67b for facilitating raise in the temperature of the mixed gas and diffusion of the mixed gas.

In the structure, before the mixed gas reaches the reforming catalyst filled space 69a, the temperature of the mixed gas is raised sufficiently and the mixed gas is sufficiently diffused by the non-reforming catalyst filled space 69b. Thus, in the reforming catalyst filled space 69a, owing to maintaining of the reforming temperature, improvement in the reforming efficiency is achieved, and it becomes possible to reliably suppress degradation of the durability due to the non-uniform flow of the mixed gas.

In this regard, an experiment for raising the temperature of the mixed gas was conducted using reforming pipes (of a comparative example) without the non-reforming catalyst filled space 69b and the reforming pipes 66

according to the present embodiment of the present

invention. The obtained result is shown in FIG. 7. The length LI of the reforming catalyst filled space 69a of the reforming pipe 66 in the axial direction is the same as the length LI of the entire reforming pipe (of the comparative example ) .

The mixed gas was introduced into the reforming pipes

66 and the reforming pipes (of the comparative example) at a predetermined initial temperature T0°C. In the reforming pipes (of the comparative example), upon receipt of the heat from the exhaust gas, reforming reaction (endothermic reaction) was started immediately. Therefore, after the temperature in the reforming pipes (of the comparative example) was lowered temporarily, the temperature was raised during reforming reaction. However, in the reforming pipes (of the comparative example), the temperature in the area downstream of a substantially central position was raised within a catalyst effective temperature range, and the reforming catalyst in the area upstream of the substantially central position was not able to effectively induce

reforming reaction.

In contrast, in the present embodiment of the present invention, after the mixed gas was introduced into the reforming pipes 66 at the predetermined initial temperature T0°C, the mixed gas was firstly supplied to the non- reforming catalyst filled space 69b, and the temperature of the mixed gas was raised while the mixed gas flowed between pellets of the non-reforming catalyst 67b. After the temperature of the mixed gas was raised to a temperature within the catalyst effective temperature range, the mixed gas was introduced into the reforming catalyst filled space 69a, and reforming reaction was started. Therefore, it became possible to effectively utilize the reforming

catalyst 67a over the entire length of the reforming

catalyst filled space 69a.

In this regard, the relationship between the ratio of the length L2 of the non-reforming catalyst filled space 69b to the length LI of the reforming catalyst filled space 69a (L2/L1) and the reforming start temperature T1°C at which reforming is started is shown in a graph of FIG. 8. As can be seen from the graph of FIG. 8, as long as 0.1 ≤ L2/L1, the reforming start temperature T1°C can be set within the catalyst effective temperature range. The L2/L1 can be set to a large value greater than 0.1. However, if the

reforming start temperature T1°C is excessively high, the temperature may exceed the heat resistance limit .

Therefore, preferably, the length of the reforming catalyst filled space 69a and the length of the non-reforming

catalyst filled space 69b should be set to values which satisfy the relationship where L2/L1 ≤ 0.2.

Further, as shown in FIG. 9, a velocity gradient of the mixed gas occurs at the inlet side in the reforming pipes 66. In this regard, the value of L2/L1 where the velocity ratio Vmin/Vmax (where Vmax denotes the maximum velocity and Vmin denotes the minimum velocity in the velocity gradient) has a predetermined value VI (where sufficiently- stirred flow is obtained) or more was measured. As a result, as shown in FIG- 10, if 0.1 ≤ L2/L1, it was detected that the mixed gas was sufficiently stirred, and then supplied to the reforming catalyst filled space 69a.

Therefore, by satisfying the relationship where 0.1 ≤ L2/L1, the mixed gas is suitably dispersed at the non- reforming catalyst filled space 69b. Thus, the entire reforming catalyst 67a in the reforming catalyst filled space 69a can be utilized effectively.

Further, the relationship between the grain size of the non-reforming catalyst 67b and the pressure loss is shown in FIG. 11. In FIG. 11, Dl denotes the grain size of the reforming catalyst 67a, and D2 denotes the grain size of the non-reforming catalyst 67b. ΔΡ denotes the pressure loss in the non-reforming catalyst filled space 69b, and ΔΡ0 denotes the pressure loss in the non-reforming catalyst filled space 69b when Dl = D2.

In FIG. 11, when D1/D2 = 0.25, ΔΡ/ΔΡ0 = 2.0, and the same effect as in the case where the length in the axial direction is doubled is obtained. Therefore, by selecting the grain size of the non-reforming catalyst 67b, for example, it becomes possible to adjust the pressure loss in each of the reforming pipes 66. In this manner, in

particular, when the pressure losses in the reforming pipes 66 are different depending on the connecting position of the raw fuel supply channel 84 with respect to the mixed gas supply chamber 78a of the reformer 46, by changing the grain size of the non-reforming catalyst 67b in any of the

reforming pipes 66, it is possible to adjust the pressure losses in the reforming pipes 66 to obtain a uniform

pressure loss distribution. In the present embodiment , the FC peripheral equipment 56 includes the first area (inner area) Rl where the exhaust gas combustor 52 and the start-up combustor 54 are provided, the annular second area (outer area) R2 around the first area Rl and where the reformer 46 and the evaporator 48 are provided, and the annular third area (outer area) R3 around the second area R2 and where the heat exchanger 50 is provided .

That is, the first area Rl is provided at the center, the annular second area R2 is provided around the first area Rl , and the annular third area R3 is provided around the second area R2. Heat waste and heat radiation can be suppressed suitably. Thus, improvement in the heat

efficiency is achieved, thermally self-sustaining operation is facilitated, and simple and compact structure of the entire fuel cell module 12 is achieved. Thermally self- sustaining operation herein means operation where the operating temperature of the fuel cell 22 is maintained using only heat energy generated in the fuel cell 22, without supplying additional heat from the outside.

Further, the reformer 46 includes the annular mixed gas supply chamber 78a, the annular reformed gas discharge chamber 78b, the reforming pipes 66, and the second

combustion gas channel 116b. The mixed gas is supplied to the mixed gas supply chamber 78a, and the produced fuel gas is discharged into the reformed gas discharge chamber 78b. Each of the reforming pipes 66 has one end connected to the mixed gas supply chamber 78a, and the other end connected to the reformed gas discharge chamber 78b. The second

combustion gas channel 116b supplies the combustion gas to the spaces between the reforming pipes 66.

Accordingly, the production cost of the reformer 46 is reduced effectively. Further, by changing the volumes of the mixed gas supply chamber 78a and the reformed gas discharge chamber 78b, the length, the diameter, and the number of the pipes, a suitable operation can be achieved depending on various operating conditions, and the design flexibility of the fuel cell module can be enhanced.

Further, the volume Wl of the reforming catalyst filled space 69a is larger than the volume W2 of the non-reforming catalyst filled space 69b. Therefore, the size of the reformer 46 is suitably prevented from increasing. Before the mixed gas reaches the reforming catalyst filled space 69a, the temperature of the mixed gas is raised

sufficiently, and the mixed gas is diffused sufficiently by the non-reforming catalyst filled space 69b. Accordingly, in the reforming catalyst filled space 69a, owing to

maintaining of the reforming temperature, improvement in the reforming efficiency is achieved, and it becomes possible to reliably suppress degradation of the durability due to the non-uniform flow of the mixed gas.

Further, the volume Wl of the reforming catalyst filled space 69a and the volume W2 of the non-reforming catalyst filled space 69b are set so as to satisfy the relationship where 0.1 ≤ W2/W1 ≤ 0.2. Therefore, before the mixed gas reaches the reforming catalyst filled space 69a, the

temperature of the mixed gas is raised sufficiently, and the mixed gas is diffused sufficiently by the non-reforming catalyst filled space 69b. Accordingly, in the reforming catalyst filled space 69a, owing to maintaining of the reforming temperature, improvement in the reforming

efficiency is achieved, and it becomes possible to reliably suppress degradation of the durability due to the nonuniform flow of the mixed gas.

Further, each of the reforming catalyst 67a and the non-reforming catalyst 67b contains ceramics as base bodies. In the reforming catalyst 67a, reforming agent, e.g., ruthenium or nickel, is supported on the base body.

Therefore, since the base bodies of the reforming catalyst 67a and the non-reforming catalyst 67b are made of the same material, reduction in the production cost is achieved suitably.

Moreover, the grain size Dl of the reforming catalyst 67a is larger than the grain size D2 of the non-reforming catalyst 67b. Therefore, the surface area of the non- reforming catalyst filled space 69b per unit area is large in comparison with the reforming catalyst filled space 69a. In the structure, before the mixed gas reaches the reforming catalyst filled space 69a, the temperature of the mixed gas is raised sufficiently, and the mixed gas is diffused sufficiently by the non-reforming catalyst filled space 69b. Accordingly, in the reforming catalyst filled space 69a, owing to maintaining of the reforming temperature,

Further, each of the base bodies of the reforming catalyst 67a and the non-reforming catalyst 67b is made of alumina. Therefore, reduction in the production cost of the reforming catalyst 67a and the non-reforming catalyst 67b is achieved suitably, and the heat mass is large. Accordingly, it becomes possible to reliably suppress the decrease in the temperature due to the reforming reaction.

Further, the reformer 46 conducts steam reforming of the mixed gas. Therefore, the present invention is suitable for steam reforming where reforming reaction is induced as endothermic reaction.

Further, the fuel cell module 12 is a solid oxide fuel cell module. Therefore, the fuel cell module 12 is suitable for, in particular, high temperature type fuel cells such as SOFC.

While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood that variations and modifications can be effected thereto by those skilled in the art without

departing from the scope of the invention as defined by the appended claims .

Claims

Claim 1. A fuel cell module (12) comprising:

a fuel cell stack (24) formed by stacking a plurality of fuel cells (22) for generating electricity by

electrochemical reactions of a fuel gas and an oxygen- containing gas ;

a reformer (46) for reforming a mixed gas of a raw fuel chiefly containing hydrocarbon and water vapor to produce the fuel gas supplied to the fuel cell stack (24);

an evaporator (48) for evaporating water, and supplying the water vapor to the reformer (46);

a heat exchanger (50) for raising a temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing gas to the fuel cell stack (24) ,·

an exhaust gas combustor (52) for combusting the fuel gas discharged from the fuel cell stack (24) as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack (24) as an oxygen-containing exhaust gas to produce the combustion gas; and

a start-up combustor (54) for combusting the raw fuel and the oxygen-containing gas to produce the combustion gas, wherein the fuel cell module includes :

an inner area where the exhaust gas combustor (52) and the start-up combustor (54) are provided; and

an annular outer area around the inner area and where the reformer (46), the evaporator (48), and the heat

exchanger (50) are provided;

wherein the reformer (46) includes an annular mixed gas supply chamber (78a) to which the mixed gas is supplied, an annular reformed gas discharge chamber (78b) to which the produced fuel gas is discharged, a plurality of reforming pipes (66) each having one end connected to the mixed gas supply chamber (78a), and another end connected to the reformed gas discharge chamber (78b), and a combustion gas channel (116b) for supplying the combustion gas to spaces between the reforming pipes (66); and

each of the reforming pipes (66) includes a reforming catalyst filled space (69a) provided on a side closer to the reformed gas discharge chamber (78b) and a non-reforming catalyst filled space (69b) provided on a side closer to the mixed gas supply chamber (78a);

the reforming catalyst filled space (69a) is filled with reforming catalyst (67a) for facilitating reforming reaction of the mixed gas; and

the non-reforming catalyst filled space (69b) is filled with non-reforming catalyst (67b) for facilitating raise in temperature of the mixed gas and diffusion of the mixed gas.

Claim 2. The fuel cell module according to claim 1 , wherein a volume Wl of the reforming catalyst filled space (69a) is larger than a volume W2 of the non-reforming catalyst filled space (69b).

Claim 3. The fuel cell module according to claim 2, wherein the volume Wl of the reforming catalyst filled space (69a) and the volume W2 of the non-reforming catalyst filled space (69b) have a relationship where 0.1 ≤ W2/W1 ≤ 0.2.

Claim 4. The fuel cell module according to claim 1 , wherein each of the reforming catalyst (67a) and the non- reforming catalyst (67b) includes a base body of ceramics, and reforming agent is supported on the base body of the reforming catalyst (67a).

Claim 5. The fuel cell module according to claim 4 , wherein grain size of the reforming catalyst is larger than grain size of the non-reforming catalyst.

Claim 6. The fuel cell module according to claim 4 , wherein the base body is formed of alumina.

Claim 7. The fuel cell module according to claim 1 , wherein the reformer (46) conducts steam reforming of the mixed gas .

Claim 8. The fuel cell module according to claim 1 , wherein the fuel cell module (12) is a solid oxide fuel cell module .